The present invention relates to a process for fully processed shelf-stable vegetables. The consumption of fruits and vegetables has taken new importance in our diet because of their role in minimizing certain degenerative diseases and in enhancing our quality of life. These plant products are low in fat and high in natural antioxidant vitamin A and vitamin C. Cao et al. (1996) indicated that based on a serving size, kale, beets, red peppers, brussels sprouts, broccoli flowers, spinach, potatoes, and corn are likely to provide the largest amount of antioxidant as determined by oxygen radical absorbency score (ORACRoo.). However, vegetables are seasonal and perishable. Moreover, vegetables typically require washing, peeling, cutting, and cooking before they can be consumed.
Various preservation methods such as freezing, canning, freeze drying, air drying, and vacuum drying are processes that prevent or minimize chemical, enzymatic, and microbial changes leading to quality loss and spoilage are aimed at extending the life and the uses of vegetables. In most instances, a frozen vegetable is closer in quality characteristics to the fresh produce than a canned or dried vegetable. A frozen vegetable is also perishable, like fresh produce, and requires the steps of thawing and cooking before consumption. A canned vegetable is shelf-stable when the cans are unopened, but canned vegetables lack fresh vegetable characteristics. Dried vegetables tend to be discolored and therefore, are not appealing. Recently developed dehydro-frozen vegetables containing 40% to 50% moisture are partially dried and frozen products. These products have more solids than the frozen or individually quick frozen (IQF) vegetables and are used in food preparations because of their ease of handling and value per pound basis. However, these vegetables also require frozen storage.
I am currently aware of two patents relevant to my high solids containing processed vegetables and the process therefore. U.S. Pat. No. 4,832,969 (Lioutas), disclosed a process using fresh vegetables for manufacturing dried green vegetables, especially broccoli florets and pea-pods. The invention is an immersion bath having five times the weight of the vegetables processed made up of buffering systems and antioxidants. The water activity of the finished product (Aw) is given as 0.3 to 0.85. The product may contain a high proportion of glycerin and salt. The very high levels of salt make the vegetables taste salty. The higher levels of glycerin potentially lead to bitterness and stickiness in the dried product. The shelf-life of the products is not clearly apparent (the color stability is given as six months) and the water activity (Aw) range indicated is very broad (0.3 to 0.85). I believe that at higher Aw (beyond 0.65), the products would need preservatives or low temperature storage to prevent microbial spoilage. To the applicant, this process appears rather cumbersome for industrial scale production as it uses a complex treatment mixture and processing steps.
U.S. Pat. No. 5,368,873 (Aebi et al.), discloses a process for preparing low moisture green bell peppers and onions by immersing the vegetables in an osmotic solution made up of high fructose corn syrup, corn syrup, glucose, fructose, maltose, sorbitol, maltitol honey, hydrogenated corn syrup or mixtures thereof. Next, the vegetables are removed and dried. This process results in heavily coated vegetables that tend to cling together when dried.
In the present invention, high solids containing vegetables are produced by immersing vegetables in a liquid of predetermined Brix until the vegetables reach a level of about 28 Brix to about 40 Brix where the liquid contains corn syrup, glycerin, and salt, removing the vegetables from the immersion, and drying the vegetables. Optionally, the vegetables may be sprayed with a vegetable oil prior to drying the vegetables. The resulting product has a high solid content and is soft, moist, and fresh-like in taste, texture, and appearance. It is also shelf-stable, microbiologically safe and ready to use.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims.
In the preferred embodiment, individually quick frozen vegetables are immersed in an immersion bath of from about 40 Brix to about 60 Brix at a temperature of from about 110xc2x0 F. to about 130xc2x0 F., for a time sufficient to bring the vegetables from a low of about 4 Brix to about 6 Brix to a level of about 28 Brix to about 40 Brix. The high solids containing vegetables are removed and preferably rinsed with a diluted immersion medium. They are then preferably lightly sprayed with vegetable oil, and then dried to a water content of about 8% to about 15% and a water activity of about 0.4 to 0.6. The soluble (sugars) solid and non-soluble (starches, celluloses, hemicelluloses, and fibers) solid content of the processed vegetables will be from about 84% to about 92%.
The Vegetables
The starting materials for the patent application are individually quick frozen (IQF) vegetables and preferably USDA grade-A vegetables. These vegetables are either diced or whole (as in the case of sweet corn or garden green peas). The use of individually quick frozen vegetables allow for the separation of the initial preparatory steps of sorting, grading, cutting, peeling, blanching, etc., that are routine plant operations involved with fresh vegetables performed at the point of a vegetable production. Using IQF vegetables affords additional flexibility. A processing plant making the high solid containing value added, shelf-stable product of the present invention does not need to be: near a vegetable growing area and the processing operations can be performed year round.
The Immersion Bath
Next, the individually quick frozen vegetables are immersed in an immersion bath, that is a liquid medium of predetermined Brix as measured on the Brix scale. The Brix scale is a hydrometer scale for sugar solutions, graduated so that its readings at a specified temperature represent percentages by weight of sugar in the solution.
The immersion processing of vegetables is intended to increase the vegetable soluble solids content from an initial low of about 4 Brix to about 6 Brix to a level of about 28 Brix to about 40 Brix, depending on the vegetable. The increased soluble solids bind with the available water content of the vegetables. Thus, the immersion manages the state and concentration of water in the vegetable. Binding and retaining this water is central to maintaining a vegetable""s shape, texture, and overall fresh-like quality. The immersion liquid also stabilizes the color of a vegetable and aids in the retention of nutrients by binding with these constituents so they may not be freely available for oxidative, enzymatic, and other degradations.
The key consideration in selecting the components of the immersion liquid here are: a natural, preservative or additive free product, the ability to maintain the natural taste and flavor of vegetables, the simplicity of handling and monitoring, recyclability, cost, and availability. Previously, chemicals, buffering systems, surfactants and antioxidants have been used. However, on an industrial scale, processes incorporating these ingredients are cumbersome to monitor and manage and the natural and preservative or additive free image of the finished product is compromised.
In contrast, the process of the present invention requires only three ingredients in its immersion solution. All are considered natural. The three ingredients are: corn syrup, glycerin, and iodized salt. Corn syrup comprises the main ingredient (about 88% to about 92%) followed by glycerin (about 6.5% to about 10.0%xe2x80x94based on the weight of immersion liquid) and salt (about 1.0% to about 2.0%xe2x80x94based on the weight of a vegetable processed).
The preferred corn syrup is designated as 62/43 product with the following properties:
Unlike high fructose corn syrup, which contain about 42% to about 95% fructose, the corn syrup used here is of lower sweetness intensity because it is high in maltose and other higher saccharides that are not as sweet as fructose or sucrose. The relative sweetness of the sugars is given as: sucrosexe2x80x941.0, glucosexe2x80x940.5 to 0.6, fructosexe2x80x941.4 and maltosexe2x80x940.3 (Griffin and Lynch, 1968). The sweetness intensity of this corn syrup is further lowered by lowering the corn syrup""s original Brix from about 82 Brix to as low as about 40 Brix, in some cases by diluting with water.
The preferred immersion medium formulation includes corn syrup, glycerin, and salt. The presently preferred formulas for each vegetable are given in example 1 to example 7.
Glycerin is used in the immersion formulas to impart soft-moist texture to the processed vegetables by its ability to bind and hold water. Sorbitol can also impart similar functionality; however. sorbitol is not as soluble in water as glycerin and is sweeter than glycerin. Consequently, it is less preferred. Sensory tests have indicated that glycerin concentrations of up to about 10% of the weight of immersion liquid do not create an oily or a metallic taste. Nevertheless, glycerin is typically expensive (80 cents per lb. vs. 10 cents per lb. for corn syrup). Therefore, at present, using a high percentage of glycerin would not only adversely affect flavor, but costs would increase as well.
The immersion solution of the present invention also employs a lower amount of salt (in most cases about 1.5% based on the weight of the vegetables) than used in earlier processes. Salt is used to moderate and balance the sweetness imparted from the corn syrup. Salt is typically not needed for sweet corn. Using lower salt levels supports the United States national policy encouraging reduced sodium intake. A high salt concentration can also alter the taste of vegetables.
The Immersion Process
The immersion process is preferably carried out either in a double-jacketed steam kettle, a circulating tank, or a tank having agitating blades. During this process, the vegetables are gently stirred, agitated, or the immersion liquid is re-circulated to increase the soluble solids by the vegetables. The weight of immersion liquid is approximately twice the weight of a vegetable being processed. A slightly higher quantity of immersion liquid than the weight of the vegetable is used to ensure the following: 1) completion of immersion process in about 1 to 2 hours; 2) reduction of surface oxidation of vegetable color from exposure to oxygen; 3) uniform agitation; and 4) prevention of damage to the vegetables during agitation. Using a higher ratio of a vegetable to the liquid is not economical from throughput standpoint.
Next, the immersion liquid is preferably heated to about 120xc2x0 F.; however, the immersion liquid temperature may range from about 110xc2x0 F. to about 130xc2x0 F. This temperature range is to make the ingredients of the immersion liquid fully soluble and also to lower the viscosity of the corn syrup. The individually quick frozen vegetables are added to the immersion liquid. After adding the individually quick frozen vegetables, the temperature of immersion liquid-vegetable mix usually drops down to between about 40xc2x0 F. to about 50xc2x0 F. The temperature of the mixture is increased to about 90xc2x0 F., typically, from a low of about 60xc2x0 F. to a high of about 90xc2x0 F., by heating the kettle, preferably, by direct steam and, in the case of a tank, by re-circulating hot water. Lower immersion temperatures for green vegetables, like broccoli, are preferred. The immersion process is monitored every hour by analyzing the Brix content of the vegetables and the immersion liquid (Table 1). When the vegetables reach a certain Brix range, the vegetables are removed from the immersion liquid and placed on a perforated stainless steel drying tray.
Rinsing
Next, the vegetables are preferably rinsed gently by spraying with a lower Brix immersion liquid (See example 1 to 7) for about 10 seconds. It thus is a diluted immersion liquid having a Brix lower than the original immersion liquid in the range of from about 20 Brix to about 45 Brix. In an industrial scale production, the rinse solution can be the same as the leftover or the spent immersion liquid. The rinsing of vegetables prevents the vegetables from clumping and matting. It also prevents surface discoloration due to exposure to air.
Spraying
Subsequent to rinsing, a thin coat of high stability oil, such as sunflower oil (calculated on the basis of 0.5% to 0.75% of anticipated dried yield) or other suitable vegetable oils, is preferably sprayed on the vegetables (except broccoli and potatoes). Oil sprayed before drying helps in making a free-flowing, non-sticky processed vegetable. In the case of broccoli and potatoes, similar results are achieved whether or not oil is sprayed on them. Consequently, since oil may affect the feel and flavor of the product, using oil to maintain the fresh vegetable appearance is not necessary, but can be used on broccoli and potatoes if desired.
Drying
Normally, about 5 lb. to about 6 lb. of a vegetable is placed on a drying tray to a depth of about xc2xd inch. The depth permits uniform heated air to be circulated across the product. In an industrial setting, the vegetables can. be dried in a continuous dryer having moving perforated steel belts. Any other suitable drying method can be used. The vegetables are dried at about 130xc2x0 F. This low drying temperature minimizes color deterioration. However, for some vegetables, such as red bell peppers, temperatures as high as 170xc2x0 F. can be used because the red bell pepper color is less susceptible to heat damage as compared to the color of, for example, broccoli. Furthermore, in the case of sweet corn, a higher drying temperature can cause protein denaturation and starch gelatinization causing gumminess and chewyness.
It is possible to dry the vegetables at temperatures lower than 130xc2x0 F., but drying at lower temperatures takes too much time to be efficient enough for large scale use of the process. In vegetables, like carrots and potatoes, the drying temperature can be raised to about 150xc2x0 F. without much effect on color, quality, or other taste and flavor characteristics. The vegetables are preferably dried using heated air. Completion of the drying process is determined by analyzing a sample of vegetables from the dryer for water activity (Table 2).
When the vegetables reach a water activity level of less than 0.6, they are taken out of the dryer and kept at ambient temperatures for about 24 hours to equilibrate prior to packaging. The equilibration is to allow the solids within the vegetables, which are in a state of flux coming out of the dryer, to stabilize so as to impart a free-flowable, non-sticky vegetable texture.
The equilibrated product is analyzed for quality before sorting, metal detecting, and packaging. The product is preferably packaged in a high-density, polyethylene lined corrugated box. The analysis for quality also includes analyzing for microbial quality (Table 3).
Because of their superior microbiological quality and the high solid content (about 84% to about 92%), these vegetables are excellent value added ingredients, particularly well suited for use in convenience and fast preparation meals. These vegetables are shelf-stable and possess comparable, similar freshness and other attributes to unprocessed vegetables.
Rehydration
Regarding rehydration, the examples show the percent rehydration data on various vegetables. Typically, in order to rehydrate the vegetables produced according to the invention, about 1 part of vegetables produced by the above process is combined with at least about 2 parts water (for example, add 2 oz water to 1 oz processed vegetables). Then, the vegetables are microwaved for at least 2 minutes (potato works better with 3 parts water and about 3. minutes heating). The vegetables may be otherwise heated (i.e., boiling on stove top), however, the cook time will vary according to the method used to heat the vegetables. Subsequently, the water is drained and the rehydrated vegetables are weighed to determine weight gain. The percent weight gain is calculated as weight of rehydrated drained vegetables/initial weight of processed vegetables xc3x97100. Typically, the rehydration weight gain is 1.5 times (or 150%) to 2 times (200%) that of initial processed weight of the vegetables made according to the present invention.